Epidemiology Kept Simple Chapter 1 Epidemiology Past Present

Epidemiology Kept Simple Chapter 1 Epidemiology Past & Present Gerstman Chapter 1 1

Epidemiology Defined • Greek roots epi = upon (as in “epidermis”) demos = the people (as in “democracy”) ology = “to speak of”, “to study” • Modern definitions of epidemiology refer to –Distributions of –Health determinants –Disease and other health-related outcomes –Populations –Application in control of health problems Gerstman Chapter 1 2

Public Health Defined • Definition of public health – organized effort – Intended to reduce of morbidity & mortality and improve health • Core disciplines public health (CEPH / ASPH) – Epidemiology – Biostatistics – Health administration – Behavioral sciences – Environmental health sciences Gerstman Chapter 1 3

Epi compared to public health • Epidemiology “study of” • Public health “organized effort” Epi = the “methodological backbone” of public health Gerstman Chapter 1 4

Basic Terms • • Morbidity = related to disease or disability Mortality = related to death Endemic = normal occurrence of a condition Epidemic = much greater than normal occurrence of a condition • Pandemic = an epidemic on multiple continents • Incidence = rate or risk of developing a condition • Prevalence = proportion of population with a condition Gerstman Chapter 1 6

Uses of Epi (Morris 1957) 1. 2. 3. 4. 5. 6. 7. Historical study Community diagnosis Working of health services Individual chances Completing the clinical picture Identify new syndromes Search for causes (paramount for prevention) Gerstman Chapter 1 7

Demographic Transition ↓ mortality ↓ fertility ↑ aging change in shape of pop’n pyramid Gerstman Chapter 1 8

Epidemiologic Transition shift from acute contagious diseases to chronic lifestyle diseases Leading Causes of Death 1900 1990 1 Pneumonia / influenza Heart disease 2 Tuberculosis 3 Diarrhea Gerstman Neoplasms Cerebrovascular Chapter 1 9

Reasons for Epi. Transition During the first half of 20 th century: • Improved standard of living • Vaccination • Improved nutrition • Sanitation and vector control During the second half of 20 th century • Birth control • Improvements in lifestyle • Medical technology (e. g. , antibiotics, treatment of hypertension, improved anesthetic safety) Gerstman Chapter 1 10

Causes of Death, U. S. , 1950– 1990 Gerstman Chapter 1 11

Mortality Trends of Selected Cancers U. S. , 1940 - 1995 • Respiratory and prostate increased • Colorectal & stomach declined • Breast cancer about the same Gerstman Chapter 1 12

Life Expectancy Trends Dramatic increases all groups Rank White women Black women White males Black men Gerstman Chapter 1 13

Selected Historical Figures & Events • Hippocrates (400 BCE) • Age of scientific enlightenment (17 th & 18 th centuries) • John Graunt (1620 – 1674) • Pierre Charles Louis (1787 – 1872) • John Snow (1813 – 1858) • Germ Theory (mid 19 th century) • Modern epidemiology (post WWII) Gerstman Chapter 1 14

Enlightenment The birth of modern medicine and public health must be studied in the context of the Western Enlightenment (pp. 11– 12). Barzun, J. (2001). From Dawn to Decadence: 500 Years of Western Cultural Life: New York: Harper. Collins. Gerstman Chapter 1 15

Demographic Approach John Graunt (1620– 74) Gerstman 17 th Century Life Table Age % surviving 6 64 16 40 26 25 36 16 46 10 56 6 60 3 76 1 80 0 Chapter 1 16

Lesson from Graunt (Rothman, 1996) • Was brief • Made reasoning clear • Subjected theories to multiple and varied tests • Invited criticism • Willing to change ideas when confronted with contradictory evidence • Avoided simplistic interpretations of data Gerstman Chapter 1 17

Germ Theory (Highlights) • Until the 19 th century, germ theory played second fiddle to vague theories of pollution (e. g. , miasma theory) • Examples of early contagionists – Fracastoro (16 th century Italian) – Henle & Koch (German physiologists) – John Snow (epidemiologist’s hero) – Pasteur (1865 experimental proof in silkworms) – Daniel Salmon (vector borne transmission) Gerstman Chapter 1 18

John Snow, Our Hero Snow’s cholera theory: • Epidemics follow routes of commerce • Agent is free-living & multiplies within the host • Transmission is water-borne, spread via fecal contamination, ingested orally • Patho-physiology: diarrhea fluid loss smudging of blood asphyxiation death Gerstman Chapter 1 John Snow (1813– 1858) 19

Snow’s Methods • Ecological comparisons: compared cholera rates by region • Cohort comparisons: compared cholera rates in exposed and nonexposed households • Case-control comparisons: compared exposure to contaminated water in cases and non-cases Gerstman Chapter 1 20

Ecological Comparisons • Southwark Water Company high neighborhoods rates • Mixed service intermediate rates • Lambeth Water Co. neighborhoods no cases Gerstman Chapter 1 21

Cohort Comparisons Water Source Southwark Lambeth Both Cases 1263 98 1422 Homes 40, 046 26, 107 256, 423 Rate per 10, 000 315 37 59 Example of calculation: Southwark rate = 1263 / 40, 046 =. 0315 = 315 / 10, 000 Gerstman Chapter 1 22

Snow’s map quasi casecontrol Gerstman Chapter 1 23

Snow’s Quasi Case-Control Analysis • Cases more likely to be exposed to Broad St. pump water than non-cases (“controls”) • Among cases: – 61 used Broad St. water, 6 did not, and 6 were uncertain • Among controls: Broad St. water use was rare – e. g. , at the Brewery (no cases) “the men …were allowed a certain quantity of malt liquor, and … do not drink water at all” Gerstman Chapter 1 24

Post-WWII (Modern) Epidemiology • Epidemiologic transition shift in focus from acute infectious diseases to chronic life style diseases • Exemplar studies – The British Doctors Study – The Framingham Heart Study Gerstman Chapter 1 25